Polishing Material Composition And Production Method Therefor

ABSTRACT

An abrasive composition to be used in an abrasive material, including an inorganic abrasive particle. The particle comprises a shell layer being an outermost layer and mainly composed of cerium oxide; and an intermediate layer comprising cerium oxide and an oxide of at least one element selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals and formed on an inner side of the shell layer. The abrasive composition also includes an organic base member comprising a polymerizable compound, wherein an outer surface of the organic base member is covered with the inorganic abrasive particle.

TECHNICAL FIELD

The present invention relates to an abrasive composition and a method of producing the same.

BACKGROUND ART

In precision polishing in process of producing glass optical elements, glass substrates, and semiconductor devices, abrasive materials composed of oxides of rare earth elements, mainly composed of cerium oxide and additionally containing lanthanum oxide, neodymium oxide, praseodymium oxide, and/or oxides of other rare earth elements, have been traditionally used. Although other abrasive materials, for example, diamond, iron oxide, aluminum oxide, zirconium oxide, and colloidal silica are also known, cerium oxide has been widely used from the viewpoint of the high polishing rate and the surface flatness of polished workpieces.

Unfortunately, cerium oxide has high specific gravity and thus has unfavorable dispersion in abrasive slurry. Furthermore, this compound has high hardness and thus aggregated oxide may cause scratches and scrapes on polished workpieces during polishing. Recent rapid trends toward reductions in size and thickness in precision electronic devices and other apparatuses have highly required precise polishing finishing with few scratches and high smoothness of the surface of a workpiece. In addition, cerium oxide is unevenly distributed over the world and is not stably supplied. Accordingly, there is a demand for developing an abrasive material that has high dispersion in abrasive slurry and can polish workpieces with high accuracy at a reduced amount of cerium oxide. In addition, although a method of collecting and recycling worn abrasive material containing cerium oxide after the use is now being developed, an abrasive material having high wear resistance and high durability is required to be developed in order to reduce costs of collection and recycle.

For example, Patent Literature 1 describes a method of preventing scratches and scrapes of a workpiece with an abrasive material that is composed of composite particles including a base material of a polysaccharide and abrasive particles containing cerium oxide and supported on the surface of the base material and exhibits improved dispersion.

Non-Patent Literature 1 describes a particle including a polymer particle core and spherical colloidal silica covering the surface of the polymer particle core.

PRIOR ART DOCUMENT Patent Literature

-   Patent Literature 1: Japanese Patent Application Laid-Open     Publication No. 2008-13716

Non-Patent Literature

-   Non-Patent Literature 1: Mater. Chem. Phys., vol. 129, pp. 871-880,     (2011)

SUMMARY OF INVENTION Problems to be Solved by the Invention

In the method described in Patent Literature 1, however, the cerium oxide particles contained in the abrasive particles have a large size and a tabular shape or cause aggregation and therefore cannot uniformly cover the surface of the base material particle. Consequently, the method has problems of scratches on the workpiece or insufficient durability.

In the abrasive material of the particles described in Non-Patent Literature 1, since the polishing rate of colloidal silica is low, a sufficient polishing rate cannot be achieved.

An object of the present invention, which has been made in view of the above circumstances, is to provide an abrasive composition that can achieve a higher polishing rate and durability and barely scratches a workpiece and can reduce the surface roughness of the polished surface at a reduced amount of cerium oxide and provide a method of producing the abrasive composition.

Means for Solving the Problem

In order to solve the above-described problems, the invention according to Aspect 1 provides:

an abrasive composition to be used in an abrasive material, including:

an inorganic abrasive particle including:

-   -   a shell layer being an outermost layer and mainly composed of         cerium oxide; and     -   an intermediate layer including cerium oxide and an oxide of at         least one element selected from the group consisting of Al, Sc,         Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd,         Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals         and formed on an inner side of the shell layer; and

an organic base member including a polymerizable compound,

wherein an outer surface of the organic base member is covered with the inorganic abrasive particle.

The invention according to Aspect 2 provides the abrasive composition according to Aspect 1, wherein

the inorganic abrasive particle further includes a core layer formed on an inner side of the intermediate layer and including a center of the inorganic abrasive particle, wherein

the core layer is mainly composed of an oxide of at least one element selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals.

The invention according to Aspect 3 provides the abrasive composition according to Aspect 1 or 2, wherein

the inorganic abrasive particle is polymerized to the outer surface of the organic base member.

The method of producing an abrasive composition according to Aspect 4 includes:

a production step of producing inorganic abrasive particles each including:

-   -   a shell layer being an outermost layer and mainly composed of         cerium oxide;     -   an intermediate layer including cerium oxide and an oxide of at         least one element selected from the group consisting of Al, Sc,         Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd,         Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals         and formed on an inner side of the shell layer; and     -   a core layer mainly composed of an oxide of at least one element         selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe,         Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm,         Yb, Lu, W, Bi, Th, and alkali earth metals and formed on an         inner side of the intermediate layer;

a dispersion step of mixing the inorganic abrasive particles produced in the production step and an organic base member including a polymerizable compound to disperse the mixture in a dispersion liquid; and

a polymerization step of adding a polymerization initiator to the dispersion including the dispersed inorganic abrasive particles and the organic base member prepared in the dispersion step to cover an outer surface of the organic base member with the inorganic abrasive particles by polymerization.

The invention according to Aspect 5 provides the method of producing an abrasive composition according to Aspect 4, wherein

the production step of producing inorganic abrasive particles includes:

a core layer-forming step of forming a core layer mainly composed of a salt of at least one element selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals through formation of the salt;

an intermediate layer-forming step of forming an intermediate layer including a Ce salt and a salt of at least one element selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals on an outer surface of the core layer by adding an aqueous solution including at least one element selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals and an aqueous solution including a Ce salt to a first dispersion including the dispersed particles of the salt of the element formed in the core layer-forming step;

a shell layer-forming step of forming a shell layer mainly composed of a Ce salt on an outer surface of the intermediate layer by adding an aqueous solution including a Ce salt to a second dispersion including the dispersed particles provided with the intermediate layer of the salts in the intermediate layer-forming step;

a solid-liquid separation step of separating the solid being an abrasive material precursor from a third dispersion prepared in the shell layer-forming step; and

a firing step of firing the abrasive material precursor prepared in the separation step in the air or in an oxidizing atmosphere.

Advantageous Effects of Invention

The abrasive composition according to the present invention can achieve a higher polishing rate and durability and barely scratches workpieces and can reduce the surface roughness of the polished surface at a reduced amount of cerium oxide.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic diagram illustrating a structure of an abrasive composition of an embodiment according to the present invention.

FIG. 1B is a schematic diagram illustrating a three-layer structure of an inorganic abrasive particle of an embodiment according to the present invention.

FIG. 2A is a graph schematically showing a composition of the three-layer structure of an inorganic abrasive particle of an embodiment according to the present invention.

FIG. 2B is a graph schematically showing a composition of the three-layer structure of an inorganic abrasive particle of an embodiment according to the present invention.

FIG. 2C is a graph schematically showing a composition of the two-layer structure of an inorganic abrasive particle of an embodiment according to the present invention.

FIG. 2D is a graph schematically showing a composition of the two-layer structure of an inorganic abrasive particle of an embodiment according to the present invention.

FIG. 3 is a schematic diagram illustrating a flow of the abrasive composition-producing process of an embodiment according to the present invention.

EMBODIMENT FOR CARRYING OUT THE INVENTION

Known abrasive materials, and inventive abrasive composition 100 and an inventive method of producing the abrasive composition 100 will now be described in detail.

<Abrasive Material>

A typical abrasive material is slurry of an abrasive composition of, for example, iron oxide (αFe₂O₃), cerium oxide, aluminum oxide, manganese oxide, zirconium oxide, or colloidal silica prepared by dispersing the composition in water or oil. The present invention relates to a novel abrasive composition 100 including an organic base member 20 covered with inorganic abrasive particles 10 mainly composed of cerium oxide that can be applied to chemical mechanical polishing (CMP) that polishes a workpiece by physical and chemical actions for achieving a sufficient polishing rate, while maintaining a flatness with high accuracy in the process of polishing a semiconductor device or glass. The present invention also relates to a method of producing the abrasive composition 100. The details will now be described.

<Organic/Inorganic Core Shell Structure of Abrasive Composition>

The abrasive composition 100 according to the present invention includes an organic base member 20 mainly composed of an organic compound and inorganic abrasive particles 10 mainly composed of an inorganic compound. That is, the inorganic abrasive particles 10 cover the exterior surface (outer surface) of the organic base member 20 to form an abrasive composition 100 having an organic/inorganic core shell structure as a whole. Specifically, as shown in FIG. 1A, a structure in which inorganic abrasive particles 10 cover the outer surface of the organic base member 20 is formed.

<Organic Base Member>

The polymerizable compound forming the organic base member 20 of the present invention can be a monomer, an oligomer, a polymer, or a mixture thereof. For example, the organic base member 20 can be poly(methyl methacrylate), polystyrene, or a polymer prepared by polymerizing at least one radical polymerizable monomer selected from, for example, methyl methacrylate, styrene, acrylic acid ester having 1 to 18 carbon atoms, methacrylic acid ester having 1 to 18 carbon atoms, methoxy(polyoxyethylene)monomethacrylate, acrylamide, dimethylacrylamide, acrolein, acrylonitrile, allylamine, vinylamine, vinyl formal, vinyl butyral, butadiene, p-vinylphenol, vinyl chloride, vinylidene chloride, 2-acrylamide-2-methylpropanesulfonic acid, vinyl alcohol, acrylonitrile, vinylpyrrolidone, vinylpyridine, vinyl acetate, and vinylimidazole.

The polymer may be polymerized using a cross-linking agent such as divinylbenzene, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, diethylene glycol diacrylate, polyethylene glycol dimethacrylate, neopentyl glycol dimethacrylate, neopentyl glycol diacrylate, 1,3-butylene glycol diacrylate, 1,3-butylene glycol dimethacrylate, trimethylolethane trimethacrylate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, tetramethylolmethane tetramethacrylate, tetramethylolmethane tetraacrylate, alkyl-modified dipentaerythritol acrylate, ethylene oxide-modified bisphenol A diacrylate, ethyl-3-dimethylaminoacrylate, ethoxydiethylene glycol acrylate, caprolactone-modified dipentaerythritol acrylate, caprolactone-modified tetrahydrofurfuryl acrylate, caprolactone-modified hydroxypivalic acid neopentyl glycol ester diacrylate, ditrimethylolpropane tetraacrylate, dipentaerythritol hexa(penta)acrylate, tetraethylene glycol diacrylate, tripropylene glycol diacrylate, trimethylolpropane ethylene oxide-modified triacrylate, trimethylolpropane acrylate, neopentyl alcohol diacrylate, 1,9-nonanediol diacrylate, 1,6-hexanediol diacrylate, 1,4-butanediol diacrylate, or pentaerythritol triacrylate.

The polymerizable compound may be a natural polymer such as a polysaccharide or a synthetic polymer. Examples of the synthetic polymer include ethylene, styrene, polyurethane, polyvinyl alcohol, and polyallylamine. Examples of the natural polymer include cellulose, chitosan, starch, and isomers of cellulose. These polymers may be used alone or in combination of two or more thereof.

Although the organic base member 20 composed of such a polymerizable compound may have, for example, a cylindrical or polygonal particle shape, preferred is a spherical shape from the viewpoint of polishing performance. Organic compounds generally have high flexibility compared to inorganic compounds. Consequently, the abrasive composition 100 including the organic base member 20 has high flexibility compared to known cerium oxide abrasive materials. The abrasive composition 100 including the organic base member 20 preferably has elasticity preventing the particle from being crushed when a pressure is applied between a workpiece and a polishing pad in a polishing process, in addition to the flexibility. The organic base member 20 preferably has an average particle diameter larger than that of the inorganic abrasive particles 10 which covers the organic base member 20 and within a range of 0.1 to 300 μm, more preferably, within a range of 0.5 to 200 μm.

The inside of the organic base member 20 may contain a compound for adjusting the specific gravity of the abrasive composition 100 in order to readily disperse the abrasive composition 100 in slurry. For example, a high specific gravity can be achieved by adding a compound such as Fe to the inside of the organic base member 20. A low specific gravity can be achieved by adding a porous material with micropores to the organic base member 20.

<Three-Layer Structure of Inorganic Abrasive Particle>

The inorganic abrasive particle 10 according to the present invention most preferably has a three-layer structure consisting of a core layer 1, an intermediate layer 2, and a shell layer 3. Specifically, as shown in FIG. 1B, an inorganic abrasive particle 10 having a three-layer structure is composed of a core layer 1 mainly composed of yttrium oxide, an intermediate layer 2 including yttrium oxide and cerium oxide on the outer surface of the core layer 1, and a shell layer 3 mainly composed of cerium oxide on the outer surface of the intermediate layer 2. For example, the core layer region 1 a of the inorganic abrasive particle 10 having a three-layer structure shown in FIG. 2A does not substantially contain cerium oxide and is mainly composed of yttrium oxide. Specifically, the core layer region 1 a may contain cerium oxide at a proportion equal to or less than that of cerium oxide contained in the intermediate layer region 2 a on the outer surface of the core layer region 1 a. The composition of the intermediate layer region 2 a varies such that the content of cerium oxide decreases from the outer side (adjacent the shell layer region 3 a) of the intermediate layer region 2 a toward the inner side (adjacent the core layer region 1 a) of the intermediate layer region 2 a at a constant concentration gradient. The intermediate layer region 2 a may contain cerium oxide at a proportion equal to or higher than that of cerium oxide contained in the core layer region 1 a and equal to or less than that of cerium oxide contained in the shell layer region 3 a. The shell layer region 3 a on the outer surface of the intermediate layer region 2 a contains cerium oxide at a proportion of approximately 100 mol %. Specifically, the proportion of cerium oxide contained in the shell layer region 3 a is preferably 50 to 100 mol %, in particular, preferably 75 mol % or more. A high polishing rate due to cerium oxide can be exhibited by increasing the concentration of cerium oxide contained in the shell layer region 3 a serving as the surface of inorganic abrasive particle 10 toward 100 mol %. The three-layer structure of the inorganic abrasive particle 10 may be one as shown in FIG. 2B. That is, in the intermediate layer region 2 a, the ratio of yttrium oxide to cerium oxide contained in the intermediate layer region 2 a is constant regardless of the distance from the center of the inorganic abrasive particle 10, for example, at approximately 1:1.

The inorganic abrasive particle 10 may have two layers: a substantially integrated layer including the core layer region 1 a and the intermediate layer region 2 a and a layer of the shell layer region 3 a mainly composed of cerium oxide. For example, as shown in FIG. 2C, the structure may have no difference between the intermediate layer region 2 a and the core layer region 1 a. That is, the inorganic abrasive particle 10 may have a structure including an intermediate layer region 2 a not having a boundary with the core layer region 1 a and including yttrium oxide and cerium oxide at a ratio of 1:1 and a shell layer region 3 a mainly composed of cerium oxide on the outer surface of the intermediate layer region 2 a. The intermediate layer region 2 a formed as the substantially integrated layer including the intermediate layer 2 and the core layer 1 may have a prescribed concentration gradient of cerium oxide. Specifically, as shown in FIG. 2D, the structure has a composition varying (the cerium oxide content decreasing) from the shell layer region 3 a side toward the center side of the inorganic abrasive particle 10 at a constant concentration gradient. An oxide including yttrium oxide, of which particles are barely broken by stress applied in use, has been described above as an example of the oxide contained in the inorganic abrasive particles 10. In addition to yttrium oxide, also preferred is an oxide of at least one element selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals. The element contained as the main component in the core layer 1 of an inorganic abrasive particle 10 is preferably an oxide of at least one element selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals and is preferably the same as the oxide of an element contained in the intermediate layer 2 for maintaining the bonding strength between the layers, but any other element may also be used. For example, the oxides contained in the core layer 1 and the intermediate layer 2 may be oxides of different elements selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals.

<Method of Producing Abrasive Composition>

An exemplary method of producing an abrasive composition 100 including an organic base member 20 and inorganic abrasive particles 10 covering the organic base member 20 will now be described. The method is given only for illustration, not limitation. In a specific embodiment, the method produces inorganic abrasive particles 10 having a three-layer structure; however, the method may be applied to production of inorganic abrasive particles 10 having a two-layer structure with an integrated layer of the core layer 1 and the intermediate layer 2.

The method of producing the abrasive composition 100 according to the present invention roughly includes the following eight steps (see FIG. 3).

1. Core Layer-Forming Step

In the core layer-forming step, a first dispersion including a dispersed basic carbonate of at least one element selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals is prepared by adding a urea compound to an aqueous solution including a salt of at least one element selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals. The salt of at least one element selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals may be, for example, nitrate, hydrochloride, or sulfate, and preferred is nitrate. Examples of the urea compound include urea, salts of urea (e.g., nitrate and hydrochloride), N,N′-dimethylacetylurea, N,N′-dibenzoylurea, benzenesulfonylurea, p-toluenesulfonylurea, trimethylurea, tetraethylurea, tetramethylurea, triphenylurea, tetraphenylurea, N-benzoylurea, methylisourea, and ethylisourea, and preferred is urea. In the core layer-forming step shown in the following embodiment, basic carbonate is formed with urea, but is merely an example, and the present invention should not be limited to the example.

The ion concentration in the aqueous solution of at least one element selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals is preferably 0.001 to 0.1 mol/L, and the concentration of urea is preferably 5 to 50 times the ion concentration. Spherical inorganic abrasive particles 10 showing monodispersion can be synthesized by controlling the ion concentration of the at least one element selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals in the aqueous solution and the ion concentration of urea within the above-mentioned ranges.

The mixture of the aqueous solutions is heated at 80° C. or higher with stirring to allow the growth of basic carbonate forming a core layer 1 dispersed in an aqueous solution (hereinafter, referred to as first dispersion).

The mixer in the heating and stirring may have any shape and other factors that can provide a sufficient stirring efficiency. In order to achieve a higher stirring efficiency, a mixer of a rotor stator type is preferably used.

2. Intermediate Layer-Forming Step

In the intermediate layer-forming step, an aqueous solution including a salt of an element selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals (which is contained in the core layer-forming step), for example, yttrium nitrate and an aqueous solution including a Ce salt are added to the first dispersion including the basic carbonate formed in core layer-forming step. Subsequently, for example, the core layer 1 is subjected to particle growth by forming an intermediate layer 2 composed of a mixture of yttrium and cerium on the outer surface of the core layer 1 composed of the basic carbonate of yttrium to increase the diameter of the basic carbonate particle. Specifically, the aqueous solution is preferably added to the first dispersion at an addition rate of 0.003 to 3.0 mmol/L per min. In particular, the proportion of Ce in the aqueous solution is preferably less than 90 mol %. If the addition rate and the proportion of Ce in the solution are outside the ranges, it is difficult to form spherical inorganic abrasive particles 10 showing monodispersion. The first dispersion is preferably heated at 80° C. or higher with stirring when the aqueous solution is added thereto at the above-mentioned rate. If the mixture is stirred at 80° C. or lower, the urea added in the core layer-forming step is not decomposed, resulting in preclusion of particle formation. The dispersion including the dispersed particles each including the intermediate layer 2 on the outer surface of the core layer 1 is referred to as a second dispersion.

3. Shell Layer-Forming Step

In the shell layer-forming step, the particles are subjected to further growth through formation of a shell layer 3 mainly composed of basic carbonate of Ce on the outer surface of the intermediate layer 2 by adding an aqueous solution including a Ce salt to the second dispersion including the dispersed particles each including the intermediate layer 2 on the outer surface of the core layer 1 formed in the intermediate layer-forming step. The aqueous solution including a Ce salt is preferably added at an addition rate of 0.003 to 3.0 mmol/L per min with stirring and heating at 80° C. or higher. If the addition rate is outside the range, it is difficult to form spherical inorganic abrasive particles 10 showing monodispersion. If the stirring is performed at 80° C. or lower, as in the intermediate layer-forming step, the urea added in the core layer-forming step is not decomposed, resulting in preclusion of particle formation. The dispersion including the dispersed particles each including the shell layer 3 on the outer surface of the intermediate layer 2 is referred to as a third dispersion.

4. Solid-Liquid Separation Step

In the solid-liquid separation step, the solid including the shell layer 3 on the outer surface of the intermediate layer 2 is collected from the third dispersion prepared in the shell layer-forming step by a solid-liquid separation procedure to obtain an abrasive material precursor. In the solid-liquid separation step, the resulting abrasive material precursor is optionally dried and may be then subjected to the firing step.

5. Firing Step

In the firing step, the abrasive material precursor of the basic carbonate obtained by the solid-liquid separation is fired in the air or in an oxidizing atmosphere at 400° C. or higher. The abrasive material precursor is converted into an oxide by the firing to give inorganic abrasive particles 10 having surfaces covered with cerium oxide.

6. Surface-Treating Step

It is not necessary, but desirable to treat the inorganic abrasive particles 10 with, for example, a silane coupling agent or titanium coupling agent for producing the hydrophobic surfaces that can readily cover the organic base member 20 including a polymerizable compound. Accordingly, the surface-treating step treats the surfaces of the inorganic abrasive particles 10 with a hydrophobic silane coupling agent, for example. The resulting inorganic abrasive particles 10 have hydrophobic surfaces having high affinity with the polymerizable compound contained in the organic base member 20 and further improve the dispersion.

The surface treatment may be performed by any process. Since the outermost surface of the inorganic abrasive particle 10 is covered by an oxide layer, an alkaline treatment of the outermost surface can readily form surface hydroxy groups, for example. The surfaces of the inorganic abrasive particles 10 can be treated through a reaction of the hydroxy group-introduced inorganic abrasive particles 10 with a silane coupling agent having a hydrophobic functional group reactive with a hydroxy group. Examples of the silane coupling agent having a hydrophobic functional group reactive with a hydroxy group include vinylsilanes, methacrylate silanes, sulfur silanes, mercaptosilanes, epoxysilanes, and phenylsilanes; specifically, γ-methacryloxypropyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, vinyltrisisopropoxysilane, vinyltris(tert-butylperoxy)silane, vinyldimethylethoxysilane, vinylmethyldimethoxysilane, vinylmethyldiethoxysilane, allyltriethoxysilane, vinyltriacetoxysilane, vinyltrichlorosilane, vinyldimethylchlorosilane, vinylmethyldichlorosilane, vinyltris(methylisobutylketoxime)silane, methylvinyldi(cyclohexanoneoxime)silane, methylvinyldi(methylethylketoxime)silane, vinyltris(methylethylketoxime)silane, 3-methacryloxypropyltrimethoxysilane, methacryloxypropyl tris(trimethylsiloxy)silane, 3-methacryloxypropyltriethoxysilane, and 3-methacryloxypropylmethyldimethoxysilane.

The silane coupling agent may be added in any amount that can partially or entirely adhere to or cover the outer surface of the organic base member 20.

7. Dispersing Step

In the dispersing step, a mixture of the inorganic abrasive particles 10 and the organic base member 20 including a polymerizable compound is dispersed in a dispersion liquid in the form of droplets of the mixture. The organic base member 20 including a polymerizable compound forms the core of the abrasive composition 100. The inorganic abrasive particles 10 are mixed with the organic base member 20 in an amount that can uniformly cover the organic base member 20. The amount is determined depending on the particle diameter of the organic base member 20.

The dispersion liquid for dispersing the mixture of the inorganic abrasive particles 10 and the organic base member 20 may be any solution incompatible with the organic base member 20. Examples of the dispersion liquid include water, methanol, ethanol, dioxane, toluene, and mixtures thereof.

For stable dispersion of the droplets of the organic base member 20 in the dispersion liquid, a stabilizer is desirably added to the dispersion liquid. Usable examples of the stabilizer include water-soluble polymers, such as starch, gelatin, arginic acid, alkyl cellulose, hydroxyalkyl cellulose, carboxylmethyl cellulose, polyvinyl alcohol, polymethacrylamide, and polyacrylic acid; water-insoluble inorganic materials, such as bentonite, talc, aluminum hydroxide, and sulfates, carbonates, and phosphates of barium, calcium, or magnesium; nonionic surfactants, such as polyoxyethylene alkyl ether; anionic surfactants, such as alkylsulfonates; and cationic surfactants, such as alkylammonium hydrochloride.

The dispersion liquid may further contain an auxiliary stabilizer, a pH adjuster, or other additives that are commonly used in suspension polymerization or emulsion polymerization.

The droplets of the organic base member 20 may be dispersed in the dispersion liquid in any manner. For example, the droplets of the organic base member 20 are added to a dispersion liquid, and the mixture is stirred. The mixing may be performed with, for example, a homomixer or a homogenizer, as well as a common mixing blade.

8. Polymerization Step

In the polymerization step of covering the organic base member 20 with the inorganic abrasive particles 10, the inorganic abrasive particles 10 are localized on the surfaces of droplets of the organic base member 20. Although the surfaces of the inorganic abrasive particles 10 are hydrophobic when they are subjected to the surface treatment in the surface-treating step, the inorganic abrasive particles 10 synthesized in an aqueous phase are oxidized to have hydrophilic surfaces. Consequently, the hydrophilic inorganic abrasive particles 10 gradually move toward the surfaces of droplets of the organic base member 20.

Specifically, the inorganic abrasive particles 10 are localized on the surfaces of droplets of the organic base member 20 by dispersing the mixture in a dispersion liquid in the dispersion step in the form of the droplets of the mixture and continuously stirring the dispersion for a given time. The stirring time is determined depending on the migration velocity of the inorganic abrasive particles 10 between the droplets of the mixture, the target shape and particle diameter of the abrasive composition 100, and other factors. Specifically, the stirring time ranges from 10 minutes to 15 hours. If the stirring time is less than 10 minutes, the inorganic abrasive particles 10 may not be uniformly dispersed on the surfaces of droplets of the organic base member 20, and the inorganic abrasive particles 10 may not form a shell structure on the outermost shell portion of the abrasive composition 100.

Subsequently, the polymerization step polymerizes the organic base member 20 and the inorganic abrasive particles 10 uniformly covering the surface of the organic base member 20 to give the abrasive composition 100. The polymerization may be performed by any common process such as emulsion polymerization, soap-free emulsion polymerization, dispersion polymerization, or suspension polymerization, and is initiated with a polymerization initiator by heating or irradiation with light. The heating temperature is determined depending on the composition and the molecular weight of the polymerizable compound contained in the organic base member 20, the type and amount of the polymerization initiator, and other factors. The polymerization is usually performed at room temperature to 100° C. Throughout the present invention, the term “polymerization” includes a reaction of forming a bond, in addition to a reaction of synthesizing a polymer. The polymerization initiator may be any initiator compatible with the polymerizable compound, and examples thereof include peroxides, such as hydrogen peroxide and benzoyl peroxide; and azobisisobutyronitrile.

Through the polymerization step, an abrasive composition 100 composed of the organic base member 20 including a polymerizable compound and the inorganic abrasive particles 10 covering the outer surface of the organic base member 20 by polymerization can be readily produced.

<Use and Deterioration of Abrasive Material>

A method of using the abrasive material will now be described by a polishing process of a glass substrate for an information recording disk as an example.

1. Preparation of Abrasive Material Slurry

A slurry of an abrasive material is produced by adding a powder of an abrasive material including the abrasive composition 100 to a solvent such as water. Aggregation is prevented by adding, for example, a dispersant to the abrasive material slurry, and the dispersion state is maintained by constantly stirring the slurry with a mixer or the like. The slurry of the abrasive material is circularly supplied to a grinder with a supply pump.

2. Polishing Step

A glass substrate is brought into contact with the upper and lower surface plates of a grinder provided with polishing pads (polishing cloth). Polishing is performed by relatively moving the pads and the glass under a pressurized condition, while the slurry of the abrasive material being supplied to the contact surfaces.

3. Deterioration of Abrasive Material

The abrasive material is used under a pressurized condition as described in the polishing step. Accordingly, the abrasive composition contained in the abrasive material is gradually disintegrated with elapse of the polishing time and are reduced in size. The reduction in size of the abrasive composition causes a reduction in polishing rate. Accordingly, an abrasive composition 100 showing a smaller change in particle size distribution between before and after the polishing are desired.

EXAMPLES

The present invention will now be specifically described by way of examples and comparative examples, but should not be construed to limit the scope of the invention in any way.

Example 1 Abrasive Material 1

Step 1. Urea was added to 10 L of aqueous yttrium nitrate (0.01 mol/L) solution into a urea concentration of 0.20 mol/L. The mixture was sufficiently stirred and was then heated at 90° C. for 1 hour with stirring.

Step 2. A pre-prepared mixture of 300 mL of aqueous yttrium nitrate (0.08 mol/L) solution and 300 mL of aqueous cerium nitrate (0.32 mol/L) solution was added to the dispersion prepared in Step 1 at an addition rate of 10 mL/min with heating at 90° C. and stirring.

Step 3. 50 mL of aqueous cerium nitrate (0.4 mol/L) solution was added to the dispersion prepared in Step 2 at an addition rate of 10 mL/min with heating at 90° C. and stirring.

Step 4. The abrasive material precursor precipitated from the dispersion prepared in Step 3 was collected with a membrane filter and was fired at 600° C. to yield inorganic abrasive particles.

Step 5. To 600 mL of toluene were added 36 g of the inorganic abrasive particles produced in Step 4 and 40 mL of 3-methacryloxypropyltrimethoxysilane. The mixture was stirred at 25° C. for 1 hour.

Step 6. The solution prepared in Step 5 was heated up to 110° C., was stirred at the temperature for 72 hours, and was then sufficiently washed with toluene and methanol and dried.

Step 7. To a mixture of 50 mL of styrene and 50 mL of ethylene glycol dimethacrylate were added 20 g of the inorganic abrasive particles subjected to surface treatment in Step 6 and 1 g of azobisisobutyronitrile with stirring to give a mixture.

Step 8. The mixture prepared in Step 7 was added to aqueous polyvinyl alcohol (4.0 mass %) solution. The mixture was stirred at 25° C. for 11 hours, was then heated up to 60° C., and was stirred at the temperature for 24 hours. The mixture was then washed with hot water of 60° C. and methanol to give an abrasive composition.

Example 2 Abrasive Material 2

Step 1. Urea was added to 10 L of aqueous yttrium nitrate (0.01 mol/L) solution into a urea concentration of 0.20 mol/L. The mixture was sufficiently stirred and was then heated at 90° C. for 1 hour with stirring.

Step 2. A pre-prepared mixture of 300 mL of aqueous yttrium nitrate (0.08 mol/L) solution and 300 mL of aqueous cerium nitrate (0.32 mol/L) solution was added to the dispersion prepared in Step 1 at an addition rate of 10 mL/min with heating at 90° C. and stirring.

Step 3. 50 mL of aqueous cerium nitrate (0.4 mol/L) solution was added to the dispersion prepared in Step 2 at an addition rate of 10 mL/min with heating at 90° C. and stirring.

Step 4. The abrasive material precursor precipitated from the dispersion prepared in Step 3 was collected with a membrane filter and was fired at 600° C. to yield inorganic abrasive particles.

Step 5. One gram of azobisisobutyronitrile was added to a mixture of 50 mL of styrene and 50 mL of ethylene glycol dimethacrylate with stirring to give a mixture.

Step 6. The mixture prepared in Step 5 was added to aqueous polyvinyl alcohol (4.0 mass %) solution. The mixture was stirred at 25° C. for 1 hour, was then heated up to 60° C., and was stirred at the temperature for 24 hours.

Step 7. To the mixture prepared in Step 6 was added 40 g of the inorganic abrasive particles prepared in Step 4. The mixture was stirred at 25° C. for 5 hours and was then washed with hot water of 60° C. and methanol to give an abrasive composition.

Comparative Example 1 Abrasive Material 3

Step 1. To 600 mL of toluene were added 36 g of a commercially available tabular cerium oxide and 40 mL of 3-methacryloxypropyltrimethoxysilane. The mixture was stirred at 25° C. for 1 hour.

Step 2. The solution prepared in Step 1 was heated up to 110° C., was stirred at the temperature for 72 hours, and was then sufficiently washed with toluene and methanol and dried.

Step 3. To a mixture of 50 mL of styrene and 50 mL of ethylene glycol dimethacrylate were added 20 g of the tabular cerium oxide subjected to surface treatment in Step 2 and 1 g of azobisisobutyronitrile with stirring to give a mixture.

Step 4. The mixture prepared in Step 3 was added to aqueous polyvinyl alcohol (4.0 mass %) solution. The mixture was stirred at 25° C. for 1 hour, was then heated up to 60° C., and was stirred at the temperature for 24 hours. The mixture was then washed with hot water of 60° C. and methanol to give an abrasive composition.

Comparative Example 2 Abrasive Material 4

Step 1. Urea was added to 10 L of water into a urea concentration of 0.20 mol/L. The mixture was sufficiently stirred and was then heated to 90° C. with stirring.

Step 2. A pre-prepared mixture of 600 mL of aqueous yttrium nitrate (0.08 mol/L) solution and 600 mL of aqueous cerium nitrate (0.32 mol/L) solution of cerium nitrate was added to the dispersion prepared in Step 1 at an addition rate of 10 mL/min with heating at 90° C. and stirring.

Step 3. The abrasive material precursor precipitated from the dispersion prepared in Step 2 was collected with a membrane filter and was fired at 600° C. to yield inorganic abrasive particles.

Step 4. To 600 mL of toluene were added 36 g of the inorganic abrasive particles produced in Step 3 and 40 mL of 3-methacryloxypropyltrimethoxysilane. The mixture was stirred at 25° C. for 1 hour.

Step 5. The solution prepared in Step 4 was heated up to 110° C., was stirred at the temperature for 72 hours, and was then sufficiently washed with toluene and methanol and dried.

Step 6. To a mixture of 50 mL of styrene and 50 mL of ethylene glycol dimethacrylate were added 20 g of the inorganic abrasive particles subjected to surface treatment in Step 5 and 1 g of azobisisobutyronitrile with stirring to give a mixture.

Step 7. The mixture prepared in Step 6 was added to aqueous polyvinyl alcohol (4.0 mass %) solution. The mixture was stirred at 25° C. for 1 hour, was then heated up to 60° C., and was stirred at the temperature for 24 hours. The mixture was then washed with hot water of 60° C. and methanol to give an abrasive composition.

Comparative Example 3 Abrasive Material 5

Step 1. To 600 mL of toluene were added 36 g of a commercially available colloidal silica and 40 mL of 3-methacryloxypropyltrimethoxysilane. The mixture was stirred at 25° C. for 1 hour.

Step 2. The solution prepared in Step 1 was heated up to 110° C., was stirred at the temperature for 72 hours, and was then sufficiently washed with toluene and methanol and dried.

Step 3. To a mixture of 50 mL of styrene and 50 mL of ethylene glycol dimethacrylate were added 20 g of the colloidal silica particles subjected to surface treatment in Step 1 and 1 g of azobisisobutyronitrile with stirring to give a mixture.

Step 4. The mixture prepared in Step 3 was added to aqueous polyvinyl alcohol (4.0 mass %) solution. The mixture was stirred at 25° C. for 1 hour, was then heated up to 60° C., and was stirred at the temperature for 24 hours. The mixture was then washed with hot water of 60° C. and methanol to give an abrasive composition.

<Evaluation of Abrasive Materials>

Abrasive materials 1 to 4 were evaluated for the polishing performance by the following method. The inorganic abrasive particles 10 synthesized in Examples 1 and 2 each had a three-layer structure including a core layer 1, an intermediate layer 2, and a shell layer 3, showed monodispersion, and had an average particle diameter of 0.40 μm and a coefficient of variation of 11%.

1. Polishing Rate

The grinder used in the polishing process polishes a workpiece surface with polishing cloth while supplying slurry of an abrasive material prepared by dispersing a powder of the abrasive material including the abrasive composition in a solvent such as water to the workpiece surface. The abrasive slurry was prepared at a concentration of 100 g/L in water (not containing any other dispersion medium). In the polishing test, a glass substrate having a diameter of 65 mm was polished under circulated supply of the abrasive slurry at a flow rate of 5 L/min, using polyurethane polishing cloth, with an abrasion tester at a pressure of 9.8 kPa (100 g/cm²) applied to the surface to be polished at a rotation rate of 100 min⁻¹ (rpm) for 30 min. The thicknesses before and after polishing were measured with Nikon Digimicro (MF501), and the polished amount (μm) per minute was calculated as the polishing rate from the change in thickness.

2. Investigation of Variation in Polishing Rate

The polishing by the method shown in “Item 1. Polishing rate” was continuously repeated five times, and the variation in polishing rate between the first time and the fifth time was investigated. The polishing rate at the first time is referred to as polishing rate 1, and the polishing rate at the fifth time is referred to as polishing rate 2. The results are shown in Table 1.

3. Observation of Scratch

A hundred glass substrates were visually inspected for scratches of about 50 to 100 μm.

4. Surface Roughness

The atomic-level surface roughness of each glass substrate was evaluated with a Dual channel ZeMapper system manufactured by Zygo Corporation.

<Evaluation of Shape and Polishing Performance of Abrasive Material>

Table 1 summarizes the results of these evaluations. In evaluation of scratch and surface roughness in polishing performance, the symbol “∘” refers to an acceptable level for practical use, and the symbol “x” refers to an unacceptable level for practical use.

TABLE 1 NUMBER OF LAYERS OF BONDING BETWEEN POLISHING PERFORMANCE EXAMPLE/ INORGANIC ORGANIC BASE MATERIAL POLISHING POLISHING ABRASIVE COMPARATIVE ABRASIVE AND INORGANIC RATE 1 RATE 2 SURFACE MATERIAL EXAMPLE PARTICLE ABRASIVE MATERIAL [μm/min] [μm/min] SCRATCH ROUGHNESS 1 EXAMPLE 1 THREE-LAYER POLYMERIZATION 0.80 0.78 ◯ ◯ 2 EXAMPLE 2 THREE-LAYER PHYSICAL ADSORPTION 0.80 0.68 ◯ ◯ 3 COMPARATIVE MONOLAYER POLYMERIZATION 0.80 0.60 X X EXAMPLE 1 4 COMPARATIVE MONOLAYER POLYMERIZATION 0.60 0.58 ◯ ◯ EXAMPLE 2 5 COMPARATIVE MONOLAYER POLYMERIZATION 0.10 0.10 ◯ ◯ EXAMPLE 3

<Evaluation of Polishing Performance of Abrasive Material>

Table 1 summarizes the results of these evaluations.

Table 1 demonstrates that the abrasive material compositions 100 prepared in Examples of the present invention have high polishing rates and excellent durability, compared to Comparative Examples, although the scratch and the surface roughness in some of Comparative Examples are equivalent to those in Examples of the invention.

Specifically, in Examples 1 and 2, the inorganic abrasive particles 10 having a three-layer structure are used in the shell portion of the abrasive composition 100 having a core-shell structure. The organic base member 20 is thus covered with the inorganic abrasive particles 10 having uniform shapes and high monodispersion and having a high surface Ce concentration. Consequently, the outer surface of the abrasive composition 100 can have a high Ce concentration, and the abrasive composition 100 shows a high polishing rate when used as an abrasive material in polishing and barely causes a reduction in the polishing rate, indicating high durability. In Comparative Example 1, since tabular cerium oxide is used, the scratch and the surface roughness are out of the ranges acceptable for practical use. In Comparative Example 2, since the inorganic abrasive particles bonded to the organic base member have a monolayer structure composed of a mixture of cerium and yttrium, the polishing rate and the durability are inferior to those in Examples of the present invention. In Comparative Example 3, since the inorganic abrasive particles are composed of colloidal silica, the polishing rate and the durability are obviously inferior to those in Examples of the present invention.

As described above, the abrasive composition 100 of the embodiment includes inorganic abrasive particles 10 including a shell layer 3 being the outermost layer and mainly composed of cerium oxide and an intermediate layer 2 including cerium oxide and an oxide of at least one element selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals and formed on the inner side of the shell layer 3; and an organic base member 20 including a polymerizable compound, where the outer surface of the organic base member 20 is covered with the inorganic abrasive particles 10. Consequently, the abrasive composition 100 can have high durability and achieve a high polishing rate at a reduced amount of cerium oxide, compared to abrasive compositions including cerium oxide not only in the outer side portion but also in the base member portion. The abrasive composition 100 includes the organic base member 20 as a base member including the center of the abrasive composition 100. Consequently, the abrasive composition 100 has a low specific gravity, compared to abrasive compositions including inorganic compounds, and can be dispersed with high stability when used as abrasive material slurry by being dispersed in water. That is, aggregation in a dispersion solvent barely occurs to reduce a risk of causing scrapes and scratches during polishing, and the surface roughness of the polished surface can be reduced.

The inorganic abrasive particles 10 can each further include a core layer 1 including the center of the inorganic abrasive particle 10 on the inner side of the intermediate layer 2, where the core layer 1 is mainly composed of an oxide of at least one element selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, N

Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals. The inorganic abrasive particles 10 thus having a three-layer structure can reduce the amount of cerium oxide and can use an element, as the core layer 1, showing high resistance against the pressure applied during polishing.

In addition, the inorganic abrasive particles 10 are polymerized to the outer surface of the organic base member 20 and are therefore barely detached, compared to physical adhesion of the inorganic abrasive particles 10 to the organic base member 20. Consequently, a reduction in polishing rate due to detachment of inorganic particles barely occurs in the polishing process.

INDUSTRIAL APPLICABILITY

The present invention can be used in the field of performing polishing with an abrasive material containing cerium oxide in the process of producing, for example, glass products, crystal oscillators, and semiconductor devices.

REFERENCE SIGNS LIST

-   -   100 abrasive composition     -   10 inorganic abrasive particle     -   20 organic base member     -   1 core layer     -   1 a core layer region     -   2 intermediate layer     -   2 a intermediate layer region     -   3 shell layer     -   3 a shell layer region 

1. An abrasive composition to be used in an abrasive material, comprising: an inorganic abrasive particle comprising: a shell layer being an outermost layer and mainly composed of cerium oxide; and an intermediate layer comprising cerium oxide and an oxide of at least one element selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals and formed on an inner side of the shell layer; and an organic base member comprising a polymerizable compound, wherein an outer surface of the organic base member is covered with the inorganic abrasive particle.
 2. The abrasive composition according to claim 1, wherein the inorganic abrasive particle further comprises a core layer formed on an inner side of the intermediate layer and including a center of the inorganic abrasive particle, wherein the core layer is mainly composed of an oxide of at least one element selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals.
 3. The abrasive composition according to claim 1, wherein the inorganic abrasive particle is polymerized to the outer surface of the organic base member.
 4. A method of producing an abrasive composition, comprising: producing inorganic abrasive particles each comprising: a shell layer being an outermost layer and mainly composed of cerium oxide; an intermediate layer comprising cerium oxide and an oxide of at least one element selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals and formed on an inner side of the shell layer; and a core layer mainly composed of an oxide of at least one element selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals and formed on an inner side of the intermediate layer; mixing the inorganic abrasive particles produced in the production and an organic base member comprising a polymerizable compound to disperse the mixture in a dispersion liquid; and adding a polymerization initiator to the dispersion comprising the dispersed inorganic abrasive particles and the organic base member prepared in the dispersing to cover an outer surface of the organic base member with the inorganic abrasive particles by polymerization.
 5. The method of producing an abrasive composition according to claim 4, wherein producing inorganic abrasive particles comprises: forming a core layer mainly composed of a salt of at least one element selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals through formation of the salt; forming an intermediate layer comprising a Ce salt and a salt of at least one element selected from the group consisting of AI, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals on an outer surface of the core layer by adding an aqueous solution comprising at least one element selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, In, Sn, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, W, Bi, Th, and alkali earth metals and an aqueous solution comprising a Ce salt to a first dispersion comprising the dispersed particles of the salt of the element formed in the core layer-forming; forming a shell layer mainly composed of a Ce salt on an outer surface of the intermediate layer by adding an aqueous solution comprising a Ce salt to a second dispersion comprising the dispersed particles provided with the intermediate layer of the salts in the intermediate layer-forming; separating the solid being an abrasive material precursor from a third dispersion prepared in the shell layer-forming; and firing the abrasive material precursor prepared in the separation in the air or in an oxidizing atmosphere. 